1. Field of the Invention
The present invention relates to a drive control method of a flow rate control valve used in a common rail type fuel injection control apparatus, and it particularly relates to a drive control method in which stability and responsiveness of a rail pressure control etc. are improved.
2. Description of the Related Art
A so-called common rail type fuel injection control apparatus is a known apparatus, as disclosed, for example, in Japan Patent No. 385114, that pressurizes fuel by a high pressure pump, pressure feeds the fuel to a common rail that accumulates pressure as an accumulator, and supplies the accumulated highly pressurized fuel to an injector. Thus, it is possible to inject the highly pressurized fuel to an engine by the injector.
In the high pressure pump of the common rail type fuel injection control apparatus, as means for controlling a flow rate of fuel to a high pressure plunger, an electromagnetic proportional control valve is used as a flow rate control valve.
It is common that this flow rate control valve adjusts a valve is opening degree by changing an amount of energization through a so-called duty ratio control that changes a pulse width of a pulse current of a constant repetition frequency. Then, the duty ratio is computed or calculated by a predetermined arithmetic expression, map etc. based on, for example, the difference between an actual rail pressure and a target rail pressure, an actual value of a current that flows to the flow rate control valve etc.
Note that, individual electrical characteristics of the flow rate control valve may easily vary depending on the way in which individual electromagnetic coils are wound etc., and the variations may cause variations of an energization current. From the perspective of reducing as much as possible the influence from such variations of the individual electrical characteristics, an integration control is used in parallel to control the energization current of the flow rate control valve.
Namely, in a known apparatus, the duty ratio of the pulse applied to the flow rate control valve is basically expressed as a percentile of the product of a target current of the flow rate control valve and a standard resistance value of the flow rate control valve divided by a vehicle battery voltage.
In other words, the duty ratio is expressed as duty ratio=target current×standard resistance value÷battery voltage×100%.
However, since an actual resistance value of the flow rate control valve changes in accordance with a temperature, a difference arises between the actual value and the standard value, and as a result, a difference is generated between an actual current and a target current. Therefore, from the perspective of making the actual current closer to the target current, regardless of such temperature changes of the resistance value of the flow rate control valve, an integral term that is calculated by successively integrating differences between the actual current and target current of the flow rate control valve is taken into account in the process of calculating the duty ratio as described below.Duty ratio=target current×standard resistance value×100%×integral term÷battery voltageHere, integral term=last integral term+integral gain×(target current−actual current).
Integral processing is taken into account in this way to control the energization current in known art also, as disclosed, for example, in JP-A-9-72453, such that the energization current of the electromagnetic proportional control valve can be controlled accurately.
However, in the known fuel injection control apparatus, a value calculated as the resistance value of the flow rate control valve is used as an initial value of the above-described integral term, the resistance value being estimated using an equation, namely, the initial value of the integral term=standard resistance value of the flow rate control valve÷fuel temperature. However, since the fuel temperature does not necessarily match a temperature of the flow rate control valve, it takes time for the actual current of the flow rate control valve to reach the target current. As a result, a problem arises in which stability and responsiveness of a rail pressure control deteriorates.
Namely, when a vehicle is operated for a sufficient period of time, it is not unreasonable to assume that the fuel temperature usually matches the temperature of the flow rate control valve. However, for example, when a vehicle is left for a long time with an ignition switch turned on and without activating a starter, and then the starter is reactivated after once turning off the ignition switch, as the flow rate control valve is energized even in a state in which the starter is not activated, the flow rate control valve is in a high temperature state, while the fuel temperature remains low. It is thus difficult to use the fuel temperature to estimate the resistance value of the flow rate control valve.